Dielectric Model Research Articles

Constrained Nuclear-Electronic Orbital Density Functional Theory with a Dielectric Continuum Solvent Model.

Solvent effects are crucial for simulating chemical and biological processes in solutions. The continuum solvation model is widely used for incorporating solvent effects with different levels of theoretical descriptions of solutes. For solutes and solutions containing hydrogen atoms, nuclear quantum effects can also be nonnegligible for reliable simulations. In this work, we couple our recently developed constrained nuclear-electronic orbital density functional theory with a dielectric continuum solvation model to cover nuclear quantum effects and solvent effects simultaneously. This approach is applied to the formate ion, where an anomalous solvatochromic shift in C-H stretch frequency was reported in experiments. By using this new approach to account for nuclear quantum effects and solvent effects, we show that the vibrational frequency of the C-H stretch and the solvatochromic shift are accurately described.

Dispersive response of polar optical phonon modes on the dielectric and size effects in a nitride nanostructure

Within the framework of the macroscopic dielectric continuum model, the dispersive spectra of polar optical phonon modes of III-nitride based nanostructures with different inner and outer dielectric media are investigated in this paper. The dielectric and quantum size effects on the dispersive frequencies of phonon modes are focused and emphasized. In the case of GaN quantum rings (QRs), we found that the dielectric constant of the inner/outer medium could significantly influence the dispersive spectra of the surface optical (SO) phonon mode as the high/low-frequency SO phonon modes are mainly localized at the inner/outer surface of QRs, respectively. Moreover, such effects associated with different crystallographic structures of GaN, i.e., the wurtzite (WZ) and zinc blende (ZB) crystal structures, are also studied in detail, showing the different degenerating behavior and electron–phonon coupling strength. The results obtained in this study provide a beneficial opportunity to independently adjust dispersive spectra of the two branches of SO modes in GaN nanostructures; thus, it could be used to design and develop phonon-based detectors and sensors.

Composite Dielectric Model for Cement Concrete Considering Water Saturation

Water has a significant impact on the dielectric constant of materials. As a multiphase composite material, the effect of water content must be taken into account when modeling the composite dielectric of cement concrete. Cement concrete traditionally has been thought of as a three-phase mixed material consisting of mortar, aggregate (limestone), and pores (air). Water was used as a constituent material of cement concrete in this paper, and its content was described in terms of water saturation. By abstracting the components of cement concrete into independent medium units and arranging them according to certain rules, the four-phase mixing model of cement concrete can be established. To investigate the effect of water, the dielectric constant of cement concrete was measured using a network analyzer at various water saturation levels. The experimental results show that water significantly can enhance the dielectric constant of cement concrete, and this effect is related to porosity: the higher the water saturation, the faster the dielectric constant increases. According to the established concrete four-phase mixed model, combined with the parallel plate capacitor theory, a composite dielectric model considering water saturation was developed which can improve the prediction accuracy under different water saturation conditions and provide a foundation for the application of ground-penetrating radar (GPR) in the quality inspection of cement concrete pavement.

Field trap effect on pool boiling enhancement in a non-uniform electric field: A numerical study

In this paper, the effect of a non-uniform electric field on pool boiling is investigated by using the pseudopotential lattice Boltzmann model and the leaky dielectric model. The focus of the study is on the field trap effect, which drives bubbles to migrate toward regions with a lower electric field intensity. Relevant results demonstrate that the non-uniform electric field effectively adjusts the distribution of dry and wet areas during boiling. Moreover, the field trap effect significantly delays the onset of film boiling by disrupting the vapor film through non-uniform electric field forces. Further, parameter analysis reveals a linear correlation between the critical heat flux and the electric capillary number (Cae). It is also determined that there exists an optimal electrode length that can achieve the best effect in delaying the Leidenfrost temperature (TL). To maximize the utilization of non-uniform effects in vapor film destruction, the hydrophilic strips are introduced to inhibit bubble coalescence and can further enhance the boiling heat transfer in this way.

Mechanical treatment of aluminum plate surfaces for improvements of capacitance and dielectric permittivity

The surface mechanical alloying (SMA) technique achieved high capacitances, improved capacitance (C) and dielectric permittivity (ε′) of mixed Aluminum/fiber-glass ‘Al/F-glass’ formed on aluminum plates. The radiofrequency RF range 0.1–106 Hz was applied on the Al/F-glass on Al plates, acting as parallel electrodes sandwiching the mixed ceramic Al/F-glass as dielectric. Capacitance increase observed after surface alloying on treated Al with small 1.5 balls than 6 mm balls on Al-plate & 1 A l-plate 2 respectively, giving twice the permittivity constant of the annealed Al. Deformation micro-scale cavities in Al surfaces played important role in raising capacitance and permittivity values; Interpreted as condensers inside a condenser caused capacitance increase according Maxwell-Wagner-Sillars effect. Dielectric relaxation model Havriliak-Negami Model was used to examine the occurrence of the Maxwell-Wagner-Sillars effect in alloyed Al/F-glass surfaces on Al plates, which confirms micro-cavities important role due to pre-treatment of Al surfaces.

Quantum Chemistry in Solution: Fiftieth Anniversary.

In this perspective, we briefly present the historical context in which, fifty years ago, dielectric continuum models were developed to incorporate solvent effects into quantum mechanical calculations. Since the first self-consistent-field equations including the solvent electrostatic potential (or reaction field) were reported in 1973, continuum models have become extremely popular in the computational chemistry community and are routinely used in a very wide range of applications.

Simulation analysis of microwave emission from lunar subsurface for SAR radiometric mode dual frequency (L/S Bands) observations onboard Chandrayaan-2

Dual Frequency Synthetic Aperture Radar (DFSAR) (at L and S bands) onboard Chandrayaan-2 (CH-2) has an experimental radiometric mode operation. This paper evaluates the utility of such experimental observations of lunar studies for the future missions. Owing the deeper penetration of L and S bands frequencies, a multilayered microwave radiative transfer model coupled with thermal model has been used to account for the microwave thermal emission or the brightness temperature (TB) from the lunar subsurface at 1.25 GHz and 2.5 GHz frequency. As the dielectric property of lunar regolith is the primary deciding factor of depth of penetration of microwaves into lunar surface, the TB simulated using different dielectric models are compared with the observed TBs of Chang′E-2/Microwave Radiometer (MRM) and selected the dielectric model which consider both frequency and metallic content (Montopoli et al. (2011); Feng et al. (2020); Siegler et al. (2020)) in this study. DFSAR/CH-2 operating frequencies such as 1.25 GHz and 2.5 GHz can be used for sounding dielectric discontinuity due to the presence of water ice, high minerals or densely packed rocky medium than thermal sounding as microwave thermal emissions at these channels are not sensitive to surface temperature, as it is invariant with time for depth below 50 cm. Hence these frequencies are potential tool to study the sub-surface characteristics such as determination of lunar regolith thickness and for the discrimination of subsurface material type.

Uncertainty evaluation of Monte Carlo simulated line scan profiles of a critical dimension scanning electron microscope (CD-SEM)

In recent years, precision and accuracy for a more precise critical dimension (CD) control have been required in CD measurement technology. CD distortion between the measurement by a critical dimension scanning electron microscope (CD-SEM) and a reference tool is the most important factor for a more accurate CD measurement. CD bias varies by a CD-SEM and a pattern condition. Therefore, it is urgently needed to identify, characterize, and quantify those parameters that may or may not affect the CD measurement by a CD-SEM. The sensitivity of the Monte Carlo simulated CD-SEM images with multiple physical modeling components has been studied previously. In this study, we demonstrate that the work function and elastic scattering potential models have a significant impact on secondary electron emission intensity, but their influence on the shape of the linescan profile is small, and other factors like the optical energy loss function and dielectric function models have even smaller effects. We have evaluated the uncertainty in the linescan profiles of Si line structures with different sidewall angles due to several different physical factors. It is found that when the CD is evaluated by a peak/valley method, the uncertainty of the CD is negligible. Therefore, it is concluded that the CD value and its related uncertainty are not critically related to the physical factors of the present Monte Carlo simulation model but rely dominantly on the line structure and electron beam parameters.

Research on detection method of concrete compressive strength based on dielectric properties

Compressive strength of concrete structures is a crucial quality parameter that determines their performance throughout lifespan. This study introduces an innovative approach of utilizing electromagnetic nondestructive testing to assess the compressive strength of mature concrete. The dielectric constant and compressive strength of standard specimens were tested by open coaxial probe and pressure testing machine, respectively, using ordinary Portland cement concrete with various water-cement ratios (0.4, 0.45, 0.5, 0.55, 0.6 and 0.65) as the research object. It has been discovered that increasing porosity reduces the number of polarized particles per unit volume of concrete, resulting in a decrease in polarization intensity. This decrease is manifested as a reduction in the dielectric constant in macro parameters. The relationship between porosity and dielectric constant was characterized using a series-parallel composite concrete dielectric model. Additionally, as porosity increases, the compressive strength of concrete decreases exponentially. By considering porosity as an intermediate variable, a concrete compressive strength model based on the dielectric constant was established. The model exhibits an average error of 3.62%, indicating the precise characterization of concrete's compressive strength using the dielectric constant. This model can serve as a theoretical basis for the implementation of electromagnetic nondestructive testing techniques in strength evaluation.

Determination of Dielectric Models Based on Effective Multi-Exponential Fittings

In high-voltage (HV) transmission and distribution systems, HV apparatuses are subjected to electrical, thermal, and mechanical stresses that deteriorate the insulation performance. The polarization and depolarization current (PDC) measurement is an effective tool used for evaluating insulation performances. The depolarization current represented by the summation of the discharge currents with the different time constants can be utilized for the development of the dielectric model based on the extended Debye’s model (EDM). This paper presents effective techniques for determining the dielectric model. Iterative approaches with predetermination of the time constants and least squares methods (either linear ordinary or percentage ones) were utilized to fit the depolarization current in the form of multi-exponential functions. The fitting parameters determined by the proposed method with the linear ordinary least squares (OLLS) method and provided by commercial software agree very well only in the high current and beginning range. Application of the linear percentage least squares (PLLS) method shows better accuracy than that of the OLLS method, and the deviation from the measured one in the low current range and the late measuring time were reduced significantly. The fitted current by this proposed technique with the PLLS method agrees well with the measured current throughout the whole recording time, even in the low current and late time range. From the accurately fitted currents, the dielectric model and the dielectric loss factors can be determined precisely, and the insulation condition of HV equipment can be evaluated properly.

An extensive theoretical quantification of secondary electron emission from silicon

Though intensive experimental studies have been carried out on electron emission properties in past decades, the reliable data from accurate experimental measurements for clean and smooth surfaces are still quite limited. In this work, we have performed a comprehensive Monte Carlo simulation of electron emission yields, the secondary electron yield (SEY, δ), backscattered electron coefficient (BSC, η) and total electron yield (TEY, σ=δ+η), from silicon and the uncertainty quantification of the theoretical calculation results for the first time. The simulations were made on total 17280 scattering models. The considered uncertainty factors in the physical modelling that can influence the calculated yields include work function data, optical energy loss function data, dielectric function models for electron inelastic scattering and the scattering potentials for electron elastic scattering. The calculation results show that δ is significantly influenced by the work function while the dielectric function model has a slight effect. Elastic scattering potential (or elastic scattering cross section) and energy loss function affects to a certain extent both δ and η. Our simulated η data agree with most of the experimental measurements while the simulated mean δ data are well below most of the experimental data. At a 75% level of confidence, the experimental σ data measured by Goto et al. lie within the uncertainty range of our simulation results. This work has provided sufficient ground for the necessity of building a theoretical database of electron emission yield considering the fact that most of the previous experimental data are not reliable due to the presence of surface contamination during the measurements.

Electrokinetic modelling of cone-jet electrosprays

The physics of electrospray has been subject to an intense debate for three decades regarding the ultimate electrokinetics that determines the electric current and the size of the emitted droplets in the steady Taylor cone-jet mode (TCJ). In order to solve with a high degree of accuracy the complete electrokinetic structure of the TCJ, in this work, we have used the full Poisson–Nernst–Planck model electrokinetic equations, which have been solved using a high accuracy numerical scheme. We consider a formulation with no interfacial adsorption of ions, as in Mori & Young (J. Fluid Mech., vol. 855, 2018, pp. 67–130). Our simulations corroborate Mori and Young's conclusion that the classical leaky dielectric model (LDM) recovers the electrodiffusion theory for weak electrolytes when disregarding ion adsorption at the interface. However, for strong electrolytes, our results differ drastically from those provided by the LDM. In this case, we observe that the ion distribution, and consequently the conductivity in the bulk, can be strongly non-homogeneous. Given the rather universal validity of the LDM experimentally observed so far, we postulate that ion interfacial adsorption must be considered in the case of strong, highly dissociated electrolytes to retrieve the LDM limit, mostly for a cone jet operating in the vicinity of the minimum flow rate.

DEVELOPMENT OF MR-BASED PROCEDURES FOR THE IMPLEMENTATION OF PATIENT-SPECIFIC DIELECTRIC MODELS FOR CLINICAL USE

Nowadays, many medical techniques are based on the application of electromagnetic fields (EMF) on human body. For the optimization of these techniques, it is necessary to understand the mechanisms of interaction between the biological system under exposure and the applied EMF. Since this interaction is described by the dielectric properties of the biological system, an accurate dielectric characterization of human body is necessary. Biological tissues are complex and heterogeneous, and their dielectric properties can vary significantly from the ex-vivo to the in vivo condition. For this reason, there is the need to measure these properties for a specific subject. Unfortunately, traditional techniques used to measure dielectric properties of tissues are not able to reach this aim and an alternative method must be devised. In this work, a model is proposed for the reconstruction of dielectric properties of biological tissues from MR acquisitions. This model is wideband, specific, applicable in vivo and useful for those medical techniques that need a precise dielectric characterization of the patients.

Flooding and inundation maps using interpolated CYGNSS reflectivity observations

Despite the myriad of remote sensing techniques currently used to map surface water, a gap remains in our ability to rapidly map inundation from flooding at the required temporal resolution to understand how floods evolve. However, the recent launch of constellations of Global Navigation Satellite System-Reflectometry (GNSS-R) satellites can provide data at a more frequent temporal repeat than a single satellite. These L-band instruments could provide moderate spatial resolution inundation maps at a better temporal resolution than other satellite radars. This paper describes a retrieval algorithm for flood inundation mapping using GNSS-R data from the Cyclone GNSS (CYGNSS) constellation. The algorithm employs a simple dielectric model to retrieve fractional inundation from an observation of reflectivity, requiring parameterizations of soil surface and water roughness as well as ancillary soil moisture data. Here, we give a brief overview of the model, describe our parameterization scheme, and present inundation maps using CYGNSS data. We describe four case studies (from the Amazon, Mozambique, Mali, and Australia) and compare the CYGNSS inundation maps to other surface water data (SWAMPS, PALSAR-2, Dartmouth Flood Observatory, MODIS, and the Global Surface Water Explorer). We identify sources of uncertainty in the CYGNSS inundation maps and discuss possible reasons for discrepancies between the inundation retrievals. We introduce the data portal, which houses the CYGNSS inundation maps, for use by the science community.

Exciton binding energy and radiation lifetime in CdTe/Cd1−xZnxS strained core/shell spherical quantum dots under pressure

In this paper, the exciton binding energy and radiation lifetime in type I and II structures of CdTe/Cd[Formula: see text]ZnxS strained core/shell spherical quantum dots under the hydrostatic pressure have been studied by using the variational method within the continuous dielectric model and effective mass approximation. The results show that for these two structures, the exciton binding energies with and without strain decrease with the increasing core radius but increase with the increasing pressure. The exciton binding energy with strain is smaller than that without strain. For type I structure, the effect of strain is small, and the radiation lifetime decreases monotonically with the increasing pressure. By contrast, for type II structure, the effects of shell radius and strain on the exciton binding energy are obvious, and the radiation lifetime increases first and then decreases with the increasing pressure.

Abnormal line loss identification system of low voltage distribution network based on HPLC communication technology

AbstractPower cable is mainly responsible for the transmission and distribution of electric energy in the power grid. The performance of a power cable greatly affects the reliability and security of the power supply. In order to solve the problem of cable aging caused by long‐term operation and various internal and external factors, this paper proposes an abnormal line loss identification method for a low‐voltage distribution network station area, aiming at focusing on the monitoring of cable aging. The transmission characteristic model based on the transmission line theory and the dielectric constant model of the aging cable insulation layer is established, and the internal relationship between the transmission characteristic and the aging characteristic is analyzed. The characteristic extraction algorithm is used to extract the characteristics of the transmission characteristic curve. Through simulation analysis, for the abnormal line loss fault, the location accuracy of different fault locations is basically at the level of 0.1–0.3%. The simulation of local defects in the cable shows that the change of material dielectric constant is more clear for the characterization of cable aging. The monitoring method in this paper is helpful to provide the relevant basis for the line maintenance plan and the operation strategy of the power grid and is of great significance to ensure the safe and stable operation of the power grid.

Terahertz Dielectric Characterization of Three-Dimensional Organotypic Treated Basal Cell Carcinoma and Corresponding Double Debye Model

The potential of terahertz (THz) spectroscopy and imaging in skin cancer detection and mainly basal cell carcinoma (BCC), the most common type of skin cancer, was previously studied. Thanks to the significant absorption of THz waves by hydrogen bonds of water and the higher hydration of tumors than normal skin, it is considered an ideal non-invasive tool for early cancer detection. Despite this potential, there is a lack of study on the THz characterization of treated tumors with anticancer drugs to constitute innovative approaches for chemotherapeutic research, and this is an inspiration for the current study. Previous THz spectroscopy measurements are based on freshly excised tissue and suffer from environmental impacts on tissue and also limit performing a thorough analysis of the effect of different biological parameters. Thus, we have cultured a three-dimensional (3D) organotypic model of BCC tumor to study the THz electromagnetic parameters of tumor in different stages along with the impact of AG1478 anticancer drug on its THz spectra. Measurements are performed in the frequency range of 0.4 to 1.6 THz, and the corresponding refractive index, absorption coefficient, and complex permittivity of normal skin, BCC, and treated BCC have been compared. Furthermore, an enhanced combinational optimization algorithm is developed to calculate the parameters of the double Debye (DD) dielectric model to explain better the discrimination of treated and untreated tumors with normal skin.

A simplified lattice Boltzmann model for two-phase electro-hydrodynamics flows and its application to simulations of droplet deformation in electric field

This paper proposes a numerical scheme within the lattice Boltzmann framework for effective simulations of two-phase electro-hydrodynamic (EHD) flows, in which the simplified multiphase lattice Boltzmann method serves as the flow solver and a leaky dielectric model is utilized to recover electric potential equation. The resultant formulations present direct evolution of macroscopic variables, due to which the present method outperforms the conventional lattice Boltzmann method in terms of memory cost and boundary treatment. Numerical validations are first carried out under the same parametric conditions as the benchmarking experimental studies with the conductivity ratio ranging from 0.03 to 1000, demonstrating that the present method is a practical and accurate tool to study large-conductivity-ratio two-phase EHD flows in scientific applications. Through the comparison with previous theoretical and numerical studies, the performance of the present method is further evaluated by varying physical parameters such as electric capillary number, electric field strength, interfacial tension, and electrical properties of liquids. The good agreements with the reference data confirm the accuracy and robustness of the proposed method. Additional studies of the dynamics of a deformed droplet in uniform electric field are carried out using the validated method. Specifically, we conduct a close numerical examination on the effect of the electrical conductivity ratio and permittivity ratio on the electric forces, and highlight the role of the dielectric electrophoretic force and the Coulomb force on the electric forces the deformation of a leaky dielectric droplet in the electrical conductivity ratio and the permittivity ratio phase diagram.

Twist-bend nematic drops as colloidal particles: Electric instabilities.

The mesogen 1,''7''-bis(4-cyanobiphenyl-4'-yl)heptane (CB7CB), doped with a small quantity of an amphiphilic compound, is examined in its biphasic state in which twist-bend nematic (N_{TB}) drops are dispersed in the isotropic fluid. Various flexoelectric and electrokinetic responses of small drops in their escaped-radial-like (ER) geometry, and also of larger ones with parabolic focal conic defects, are discussed. A pair of confocal parabolas with their axes along the applied low-frequency electric field undergo periodic dimensional changes so as to contribute flexoelectrically to free-energy reduction. In an ER droplet, the same result is achieved by periodic relocations of the hedgehog core. Sine-wave fields of low frequency and high voltage excite patterned states near zero-voltage crossings and homeotropic alignment at peak voltages. ER drops also exhibit electrohydrodynamic effects; in relatively weak fields, they undergo translatory motion with a velocity that is a quadratic in the field strength; the drift, which occurs over a very wide frequency range, extending from dc to MHz region, is enabled by radial symmetry breaking that their off-centered geometry entails; and the drift direction reverses across a critical frequency. In high fields, vortical flows occurring within an ER N_{TB} drop become discernible. The hydrodynamic effects are discussed based on the Taylor-Melcher leaky dielectric model.

Raman scattering study of photoexcited plasma in GaAsBi/GaAs heterostructures: Influence of carrier confinement on photoluminescence

GaAsBi alloys are potential candidates for near-infrared optoelectronic applications, such as light-emitting diodes, laser diodes, avalanche photodiodes, and solar cells. In this paper, photoexcited plasma in GaAs1-xBix/GaAs (1.7 ≤ x ≤ 8.6%) heterostructures grown by molecular beam epitaxy was investigated using Raman spectroscopy. The strong LO phonon-plasmon coupled mode (LOPC) was generated by continuous-wave laser excitation at room temperature. The upper branch of the LOPC mode (L+ mode) was clearly observed for Bi contents from x = 3.9–8.6%, which indicates that photoexcited carriers with relatively good carrier mobility were confined in the GaAsBi/GaAs heterostructure. The photoexcited carrier density that was obtained by line shape analysis of the Raman spectra based on a dielectric model increased as the Bi content increased from 1.7 to 6.4%. This indicates that carrier overflow from the GaAsBi layer was suppressed because of the larger conduction band offset at the GaAsBi/GaAs heterointerface. In addition, the optical mobility calculated using the damping constant of the photoexcited L+ mode gradually decreased with increasing Bi content. This may be attributed to an increased defect density with decreasing growth temperature. Our findings provide valuable insight into the development of high-performance optoelectronic devices based on GaAsBi alloys and show the potential of Raman spectroscopy for evaluation of carrier confinement in heterostructures.